Heretofore, the illuminated-type push-button switch has been utilized for an input unit of a mobile communication device, etc. In the member for lighting a push-button switch of this type for input units, lighting functions which act as illumination function to illuminate a function display portion of the push-button switch at night-time are widely used.
FIG. 2 shows an example of a conventional illuminated-type push-button switch. As shown in FIG. 2, in the conventional push-button switch used for an input unit of a cell phone, etc., a cover base 32, which is formed in one body with a key top portion 31 that constitutes an operation key, and a circuit board 33 are disposed in a face-to-face manner and assembled in a housing of the input unit, so as to realize a switching function of the push-button switch 30. The push-button switch 30 has a display portion 34.
On the circuit board 33, a light source such as LED 35, etc., is provided. Light from the light source or reflected light thereof goes from an underside portion to an upper surface portion of the key top portion 31, so that even at night-time a display of the cell phone can be visually recognized easily.
The applicants of the present application already filed a patent application relating to a push-button switch member whose display portion is illuminated without such trouble as uneven brightness, with smaller power consumption, thinner in thickness and lighter in weight and method for manufacturing the same. It has a built-in EL element made from electroluminescent material. (Japanese patent publication JP-A-2002-367469).
In another prior art, an illuminated type sheet-like key top is disclosed. It comprises a light-transmitting resin film on a body of a key top portion, an organic polymer layer as a transparent electrode layer on a lower surface of the resin film, a compensating electrode layer, a light-emitting layer, a dielectric layer, a counter electrode layer and an insulation layer (Japanese Patent Publication JP-A-2000-285760).
In still another prior art, a push-button switch member for an input unit of cell phone, etc., has an illuminating display portion disposed on an upper surface side of the key top. And an EL sheet having a self-emitting type sheet-like light-emitting portion is used at the display portion. The push-button switch member with such EL sheet can be obtained by forming the EL sheet into a key top shape. The EL sheet has the sheet-like light emitting portion comprising a transparent electrode layer having an electroconductive polymer of a colored layer formed on a transparent insulation film, a light-emitting layer made of inorganic EL, etc., a dielectric layer and a counter electrode layer. All layers are laminated in this order. (Japanese patent publication JP-A-2004-6105).